Ultrafast electron hole plasma dynamics in chemically pristine and Ag-doped ZnO nanorods

The ultrafast dynamics of femotosecond laser excited carriers in the assembly of chemically pristine and Ag-doped ZnO nanorods is studied using the two-color pump-probe spectroscopy technique with the central photon energy of the pump pulse equal to the bandgap of the nanorods ensemble ( ∼3.14 eV) and the central photon energy of the probe pulse kept at 1.57 eV. On photo-excitation at 3.14 eV with an excited carrier density of ∼ 10 20 cm − 3, about an order higher than the Mott density of bulk ZnO, the time delayed probe transmission displays tri-exponential decay exhibiting three decay mechanisms: (i) ultrafast electron-phonon thermalization of the order of ∼0.40 ps, (ii) trap mediated decay with a time constant of ∼9 ps, and (iii) e-h recombination with a time constant of ∼650 ps. It is observed that as the carrier density increases, the first two decay processes get longer on contrary to the recombination time which gets shorter. A detailed analysis of the faster decay process through the Two Temperatu...